The present invention relates to an ink dot printer comprising a means for storing magnetic ink, a pair of magnetic pole plates arranged opposite to each other to form a slit whose one end is immersed in magnetic ink supplied from the magnetic ink storing means, a magnetism generating means for magnetizing the pair of magnetic pole plates to introduce magnetic ink supplied from the magnetic ink storing means into the slit and form a magnetic ink film in the slit, a plurality of needles arranged adjacent to one another along the longitudinal direction of the slit and each freely movable in the longitudinal direction of the needle between a first position where its one end portions are immersed in the magnetic ink film in the slit formed by the paired magnetic pole plates and a second position where its one end portions are projected from the magnetic ink film in the slit, and a driving means for selectivly driving the needles to move between the first and second positions, wherein the one or more needles selected force magnetic ink, which has been stuck on their end faces of the one end portions at the first position, onto a recording paper at the second position to form dots of magnetic ink on the recording paper so as to print symbols such as characters or numerals on the recording paper by the grouping of these dots.
The wire dot printer or thermal printer which is usually used these days is the ink dot printer. The wire dot printer selectively drives needles whose tips directly strike a pressure-sensitive manifold paper on a platen or whose tips indirectly strike a recoding paper on the platen through an ink ribbon interposed between the tips of the needles and the recording paper. In this fashion, dots are formed on the pressure-sensitive manifold paper or recording paper to print symbols such as characters or numerals by the grouping of these dots. In this conventional wire dot printer, however, a large amount of noise is caused when the symbols are printed onto the pressure-sensitive manifold paper or recording paper. In addition, no other paper except for the pressure-sensitive manifold paper can be used. Further, the expensive ink ribbon of the latter method must be changed frequently. The expensive ink ribbon also must be used in the thermal printer.
In order to eliminate the drawbacks of the conventioal wire dot printer or thermal printer, there have been proposed various kinds of ink dot printers wherein magnetic ink is stuck on the end faces of the front end portions of the needles and wherein these needles are driven selectively to transfer the magnetic ink onto the recording paper to form dots thereon. In the case of these ink dot printers, however, the end faces of the front end portions of the needles must be appropriately positioned relative to the recording paper on the platen when the magnetic ink is transferred from the end faces onto the recording paper on the platen. It not, the end faces of the front end portions of the needles strike the recording paper on the platen too strongly, as in the case of the conventional wire dot printer, thus generating too much noise. In addition, the dots of the magnetic ink transferred onto the recording paper are scattered by the excessive force of the end faces striking the paper, thus making the contour of the dots blurred. Adjusting the distance of the needles from the platen troublesome task, and must be frequently repeated since the needles are repeatedly driven.